Rubber chemicals are taken in this document to be substances which are added to rubber compounds to allow vulcanisation to occur, to control the course of vulcanisation and to influence the properties of the vulcanisates. Rubber chemicals are usually powders which may not be readily incorporated homogeneously into rubber compounds and usually give rise to dust during processing. Rubber chemicals are therefore often used in bound, dustless form in order to avoid dust problems, to accelerate incorporation and to improve the homogeneity of the compound.
It has proved particularly favourable to use rubber chemicals in rubber-bound form as master batches. Suitable binders are EPDM rubber, ethylene/vinyl acetate copolymer rubber or mixtures of the two. These master batches, which are often in pellet form, frequently contain plasticisers and dispersion auxiliaries in addition to rubber chemicals and rubber.
Another type of bound rubber chemicals uses factice or similar materials, for example epoxidised triglycerides crosslinked with dicarboxylic acids (German patent application P 39 20 411), as binder.
In order to produce these master batches from rubber chemicals, optionally auxiliary substances and the polymeric binders, it is necessary to perform mixing in customary mixing equipment, for example closed mixers, extruders or rollers, and then to convert them into a form suitable for use, for example pellets. The mechanical mixing processes do not guarantee complete homogeneity, particularly since the rubber chemicals have a tendency to reagglomerate.